Metamorphic T-X Phase Diagrams

Click on an image or the link in the caption, and a PDF file of the diagram will download to your computer. Some of the PDF files are animations – they contain more than one page that can be shown in sequence to see changes as temperature or some other variable changes.

Unless otherwise noted, these figures were drafted by Dexter Perkins or John Brady.

CaO-MgO-SiO2-H2O-CO2

TX diagram showing some reactions in the system CaO-MgO-SiO2-H2O-CO2. These reactions intersect at invariant points that involve other reactions not shown. Portions of some of the reactions shown are metastable.
Download PDF(Acrobat (PDF) 17kB Jun8 07)

TX diagram showing some reactions in the system CaO-MgO-SiO2-H2O-CO2. These reactions intersect at invariant points that involve other reactions not shown. Portions of some of the reactions shown are metastable. For clarity, reaction coefficients have been omitted. H2O and CO2 are not listed as products or reactants. Their involvement must be inferred. Note that reactions involving H2O (or CO2) can never reach the H20 (or CO2) side of the graph. The one reaction that involve neither H20 nor CO2 plots as a straight horizontal line.
Download PDF(Acrobat (PDF) 15kB Jun8 07)

TX diagram for the system CaO-MgO-SiO2-H2O-CO2. All stable reactions are shown. There are two invariant points at about 600 oC.
Download PDF(Acrobat (PDF) 17kB Jun8 07)

TX diagram for the system CaO-MgO-SiO2-H2O-CO2. All stable reactions are shown. There are two invariant points at about 600 oC.
Download PDF(Acrobat (PDF) 17kB Jun8 07)

Three examples of how fluid might be buffered by T-X equilibria. The different results arise because the ratio of fluid:minerals and the amounts of the various minerals present are different in each case. In #1, the volume of fluid is so large that the mineral reactions lead to no appreciable change in fluid composition. In case 2, the fluid initially becomes more CO2 rich (becuase formation of Tr consumes H2O while using up CO2) as temperature increases. After reaching point D, however, tremolite begins breaking down, so fluid becomes more H2O rich until all tremolite is gone. In case 3, fluid starts out becoming more CO2 rich, but quartz is exhausted before point D is reached. So, temperature increases with no change in fluid composition untile the (Qz) curve is reached. Then, fluid becomes slightly more H2O rich until, finally, the tremoite is all gone.
Download PDF(Acrobat (PDF) 14kB Aug14 07)

Other

TX diagram showing reactons involving K-feldspar, diopside, calcite, phlogopite, quartz and tremolite. This drawing is theoretically correct but may not represent reality. It serves to show how the same invariant point can appear twice on a phase diagram. It is based on a figure from John Valley's (1980) dissertation.
Download PDF(Acrobat (PDF) 12kB Aug14 07)